1. Field of the Invention
The present invention relates to a method and an apparatus for joint phase and frequency offset estimator for a multiple phase shift keying (referred to as “MPSK” hereinafter) transmission, which is capable of generating a smaller delay in comparison with a conventional method sequentially estimating the phase and frequency offsets by simultaneously performing phase and frequency offset estimations using phase estimates computed from the samples within each sliced observation interval, and which is capable of reducing a complexity by sharing a plurality of hardware parts.
2. Description of the Prior Art
In recent years, a synchronization technique is variously required in transmitting and receiving signal processes of a digital communication. The synchronization techniques can be classified into a burst synchronization and a continuous synchronization. Many modern digital communication systems utilize a burst mode transmission in which a relatively small number of information bits are transmitted by sending a sequence of a small number of waveforms. In a general burst packet transmission, the transmitting data are divided into packets, a short preamble symbol sequence is attached at the beginning of each packet, and then a receiver demodulates the received symbols with an achievement of a synchronization by using the short preamble.
Data are transmitted using a burst mode in a time division duplex (referred to as “TDD” hereinafter) mode transmission of a fixed broadband wireless access (referred to as “BWA” hereinafter) system. Since the fixed BWA system utilizes a coherence communication, it should compensate for a phase offset and a frequency offset. The phase offset is caused by disparity in the reference phases of a remote transmitter and a local receiver. The frequency offset is caused by disparity in the frequencies of the remote transmitter and the local receiver. Accordingly, the frequency offset and the phase offset should be necessarily compensated. In the burst mode communication, a short preamble is appended in front of a starting part of each burst transmission and the burst having the short preamble is transmitted. In order to obtain a frequency offset and a phase offset, a feed-forward synchronous method is generally used.
In a typical system, the phase offset and the frequency offset are independently estimated. Namely, two exclusive hardwares causing a structural complexity are used to estimate the phase offset and a frequency offset, i.e., a maximum likelihood phase estimator is used to estimate the phase offset estimation and a data-aided frequency offset estimator is used to estimate the frequency,offset estimation. Since a phase offset estimation starts after a compensation of a frequency offset, a latency is increased in a demodulator.
Conventional apparatus and method for estimating a frequency and a phase calculates phases on every received symbols, and then estimates a phase offset and a frequency offset by using the calculated phases. To obtain a phase offset, the calculated phases are summed up, and the sum of the calculated phases is divided by a predetermined value. To obtain a frequency offset estimate, a total N symbol observing interval are divided into three even length intervals. The phases of the first observing interval are multiplied by a negative constant, the phases of the second are multiplied by zero, and the phases of the third are multiplied by a positive constant having the same amount as the negative constant in first symbol observing interval. The resultant values of the multiplications in the first, second, and third intervals are summed up and the result is divided by a predetermined value, thereby estimating a frequency offset.